The dual active-bridge (DAB) converter plays a key role in bidirectional energy transfer applications, with single-phase-shift (SPS) control being the most common control mode. However, when the input and output voltages of the DAB converter are mismatched, significant circulating power is generated leading to higher current stress, while zero-voltage-switching (ZVS) cannot be achieved for all switches in light load conditions. To address the efficiency degradation of traditional SPS control when there are voltage mismatches, an optimized dual-phase-shift (DPS) control strategy is proposed. This ensures minimum backflow power of all switching tubes and ZVS in the full power range, thus improving the efficiency of the converter with a wide voltage regulation ratio. First, considering the power transfer characteristics, voltage regulation ratio, coupling relationship between minimum backflow power, minimum current stress and full ZVS, the power range of all switches to achieve ZVS is studied. Then, from the given constraints, a global optimal solution is obtained by segmented optimization. Finally, an experimental platform is set up to verify that, the proposed optimization strategy can achieve ZVS of all switches in the full power range when there are voltage mismatches, and at the same time, effectively reduce the backflow power.